Explicitly specify the ui::Compositor to DelegatedFrameHost

ui/compositor/compositor_observer.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_COMPOSITOR_COMPOSITOR_OBSERVER_H_
 #define UI_COMPOSITOR_COMPOSITOR_OBSERVER_H_
 
 #include "base/time/time.h"
 #include "ui/compositor/compositor_export.h"
 
@@ skipping 23 matching lines @@
   // Called when compositing completes: the present to screen has completed.
   virtual void OnCompositingEnded(Compositor* compositor) = 0;
 
   // Called when compositing is aborted (e.g. lost graphics context).
   virtual void OnCompositingAborted(Compositor* compositor) = 0;
 
   // Called when the compositor lock state changes.
   virtual void OnCompositingLockStateChanged(Compositor* compositor) = 0;
 
  protected:
-#if defined(OS_MACOSX)
-  // Debugging instrumentation for crbug.com/401630.
-  // TODO(ccameron): remove this.
+  // Instrumentation to ensure that observers are not left attached after they
+  // are destroyed.
   friend class Compositor;
   int32 observing_count_;
-#endif
 
   virtual ~CompositorObserver();
 };
 
 }  // namespace ui
 
 #endif  // UI_COMPOSITOR_COMPOSITOR_OBSERVER_H_